Segmental retaining walls are a category of earth retention systems that utilize modular, dry stacked, pre-cast concrete blocks to create a stable mass with sufficient weight to resist earth pressures developed by the adjacent soil.
The modular, segmental retaining wall units (SRW blocks) vary in shape and size. Smaller units can be placed by hand (up to 80 lbs) using manual labour. It has been our experience that landscape and construction contractors are having an increasingly difficult time finding reliable manual labourers to install hand placed blocks.
As such, machine placeable units are becoming more and more popular each year. Machine placeable units are SRW blocks that are too large (heavy) to be placed by hand, and require the use of heavy construction machinery (backhoe, crane, etc.) that is outfitted with a specialized clamping device to move them.
As will be explained hereinafter, the present invention is actually an improvement to the existing scissor clamps of which the basic structure is disclosed below, which improvement is adapted for use in combination with a new SRW unit that has been designed to accommodate it.
Existing scissor clamps are actually mechanical devices, normally fabricated from structural steel components, that are designed to securely hold and lift construction materials. These clamps are commonly used to handle individual concrete retaining wall units, concrete pavers, building blocks, etc.
These clamps use freely rotating pin connections to create a scissor configuration with a system of structural steel elements.
The “arms” of each scissor clamp are configured to rotate towards each other about two fixed points in reaction to the clamp being lifted vertically from the midpoint. The arms rotate inwards and generate a compression force on the object to be lifted. At the interface between the object (concrete unit, block) and the clamp arms are rubberized pads. The compression force generated as the clamp arms rotate towards each other results in friction between the object and pads. The frictional force is sufficient to securely hold the self weight of the object, and prevent it from slipping out of the clamp. Essentially, the self weight of the clamp and block is used to generate this clamping action.
With the concrete block held securely in place, the construction machinery is able to lift and move the clamp and object from point to point.
In the context of machine placed segmental retaining walls, the existing scissor clamps have been designed to pick up one (1) unit at a time. Most commonly, each scissor clamp is oriented perpendicular to the unit, and the pads are facing the front and back of the block.
In most cases, the units arrive at the site in bundles on large wood pallets. The units are normally facing each other on the pallet.
In order to pick an SRW block up from the front and back face (perpendicular orientation to the block) using the existing scissor clamp as described above, the SRW blocks on the pallet must be separated to allow the clamp to slide into place. This is often done by a worker using a crow bar and can be difficult and time consuming.